1. Field of the Invention
The present invention relates to moulded articles, especially optical lenses, based on an organically modified siloxane condensation product, to the use of said moulded articles, and to a method of preparing such moulded articles.
2. Discussion of Background Information
High-performance optical lenses are generally made of inorganic glass because inorganic glass provides high optical quality by homogeneous melting processes, high thermal stability, especially in combination with high-power light sources, which are used for instance in cars, and high shape stability even at temperatures of up to 200° C. However, a serious disadvantage is the high specific weight of such lenses resulting in heavy-weight optical systems, e.g. headlights of automotive applications. Thus, the weight of two headlights easily add up to more than 1 kg. Because any additional weight in a car leads to considerable increase of fuel consumption, weight reduction in headlights is an important target for new optical system developments.
In order to substitute inorganic glasses having densities of 2.2 to 2.5 g/cm3 by components having lower densities, highly transparent organic polymers have been considered. However, the demands of temperature stability, UV and light stability as well as temperature independent shape stability could not be solved in the past. In addition, materials suitable for high throughput forming technologies are required. A mechanical shaping such as grinding and polishing is time-consuming and hence impractical. Thermoplastic polymers such as PMMA or PC can be processed by injection moulding techniques, but their thermal and/or UV stability is insufficient. Other known polymers do not enable high throughput moulding techniques. Silicones exhibit sufficient temperature stability, however, easy to mould silicones are more or less rubber-like and do not satisfy the requirements to shape stability. It is to say that at present no technical polymers are available for this purpose which meet with the demands discussed.
Thus, an object of the present invention is to provide a material suitable for light-weight high-performance optical lenses for transportation purposes, especially headlights for automotive applications, and a respective fabrication process which is cost-effective and allows a high throughput.